In the field of color television, undesired variations in television receiver reception is frequently due to variations in the signals provided for reception. Normally, undesired signal variations are either of the form wherein both color burst and chroma signals simultaneously vary or of the type wherein the ratio of color burst to chroma signals undesirably varies.
In the first instance, simultaneous burst and chroma variations are frequently due to either the signal as broadcast or to a multipath propogation of the broadcast signal. In the second instance, color burst to chroma signal ratio variations are usually due either to deterioration of the signal ratio in the broadcast apparatus or to re-insertion of the color burst signal by a local station.
As to minimization of the simultaneous color burst and chroma variations, an automatic chroma control (ACC) is usually employed in a manner such that the chroma level is automatically varied in accordance with variations in the color burst signal. While such a system provides a desirable result for simultaneous color burst and chroma signal variations, it can be readily understood that the adjustments obtainable therefrom are highly undesirable when the ratio of the color burst to chroma signal undesirably varies. Factually, such corrective circuitry is deleterious and magnifies rather than reduces the undesired errors when the variations are concerned with the ratio of the color burst to chroma signal.
One known attempt to remedy the undesired variations in reception due to a shift in the color burst to chroma signal ratio includes the use of an average detector system to control the gain of a color amplifier stage. However, average detection does not maintain the desired peak values of chroma signal whereupon an undesired "washed-out" or an over-saturated condition is obtained.
In another known technique, undesired color burst to chroma signal ratio variations are applied to circuitry which utilizes both average and threshold detectors. As set forth in the above-mentioned application, Ser. No. 260,660, the average and threshold detectors track in a manner such that a substantially constant value of chroma is provided regardless of the type of scene viewed.
Although the above-mentioned circuitry has been and still is employed to improve television receiver reception, it has been found that there still exists room for enhanced signal reception. In other words, noise-free reception of signals truly representative of peak chroma signals with inexpensive circuitry employing a reduced number of discrete components is an obviously desirable goal.